The pith lines need to merge before ground level for something to be considered a single trunk tree. If there is more than one pith line at ground level it is a multitrunk tree. If there is only one pith at ground level then it is a single trunk tree. Low branches could come out below 4.5 feet, but above the ground and the tree still be a single trunk tree.

In the tree measuring guidelines, (all three of the documents, the original version, the one published in the Bulletin, and the updated version) Will Blozan writes:

"I use a “pith test” to define what a multitrunk tree is. If the tree has more than one pith at ground level it is a multiple-stemmed tree. Note I did not say 4.5 feet above the ground. This is because the 4.5 foot height is a forestry standard and is an arbitrary and convenient place for most people to measure a tree. Some trees, like flowering dogwood or rhododendrons, may branch well below 4.5 feet but have a single pith at ground level. In the case of such trees, I would measure the narrowest point below the lowest fork. More detailed discussions of how to measure multitrunk trees and trees with other odd forms is presented on the ENTS website."

Ed Frank

"I love science and it pains me to think that so many are terrified of the subject or feel that choosing science means you cannot also choose compassion, or the arts, or be awe by nature. Science is not meant to cure us of mystery, but to reinvent and revigorate it." by Robert M. Sapolsky

I know this is not really practical, but it seems to me that theoretically you could compare the DNA from core samples of the leader and main trunk to determine if they were the same tree or two fused trees. I have been amazed at how much a double pine that has fused can look like a single trunk tree. In my tree work I occasionally find that a tree is a double only after it is cut down. Sometimes this can be dangerous, as not much may be holding one part of a tree after a felling notch is made, thus one section of the tree may go prematurely and possibly the wrong way as mostly it is being held by bark. This scenario is exceedingly rare though, and when there is any doubt I rig both sections of the tree ahead of time.

There is a basic misconception here. We are not defining whether something is a single or multitrunk tree based on genetics. The multitrunk tree may be growing from the same root mass and have identical DNA in all of its trunks. For measurement purposes we are classifying a multitrunk tree as a different measurement category than a single trunk tree because of its growth pattern, not because of different genetics. There may be some cases where there actually are two different specimens of the same species of tree growing together to form a fused mass, but these would be I would guess an extremely rare circumstance. There are occasional examples of two different species growing together - the Hugging Trees in the multitrunk tree classification scheme I previously proposed http://www.nativetreesociety.org/multi/index_multi.htm. I would expect that hugging trees of different species would be more common than two different trees from the same species.

Are there some good keys that help you identify when something really is a double that looks like a single trunk tree, or whether it is in fact a single trunk that others might not be aware? As you say sometimes you can't tell until the tree is cut down, but are there hidden indicators in other cases you might notice if searching for them?

Ed

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"I love science and it pains me to think that so many are terrified of the subject or feel that choosing science means you cannot also choose compassion, or the arts, or be awe by nature. Science is not meant to cure us of mystery, but to reinvent and revigorate it." by Robert M. Sapolsky

Trees are funny organisms. Regarding measurement I fully concur with Will and Ed that we should not give official blessing to two or more trees masquerading as one, and I do approve of the measurement criteria that NTS has developed in terms of deciding how many trees one is measuring. That said, in a more philosophical vein, some scientists consider a large grove of aspens to be a single organism because they may be connected by roots and sometimes, the entire grove consists of clones having essentially the same DNA. This seems more an argument about the nature of some trees and whether trees, which tend to reiterate their growth pattern in each twig, are colonial organisms or individuals. Also it is interesting that, some Lacertid lizards which are parthenogenic (in this case having no males) and hence having clonal offspring, are considered separate individuals. Botanist Francis Halle discussed this in his wonderful 2002 book In Praise of Plants. I guess its just different ways of looking at the same thing rather than having clearly contradictory and competing facts, but it seems to be a reasonable analogy to what Ed was explaining to me. Sorry, just mental masturbation here, probably distracting from the main thread.

You should also mention that the HWA are all female and reproduction is parthenogenic. I don't think you would get much argument to the proposition that many of the mutitrunk trees are single organisms, the criteria were are considering is the question of what is a tree? If we define a single trunk as a tree, then a multitrunk cluster, even though they are all part of the same organism, should be considered multiple trees that have grown together. A large clonal colony like Pando may be a single organism, but that organism consists of many trees. It is a way of organizing information, so that you are comparing like features to like features, single trunk growth to single trunk growth. Your left hand and fingers are all part of one organism that consists of one hand and five fingers.

Ed

"I love science and it pains me to think that so many are terrified of the subject or feel that choosing science means you cannot also choose compassion, or the arts, or be awe by nature. Science is not meant to cure us of mystery, but to reinvent and revigorate it." by Robert M. Sapolsky

Exactly, I agree completely, as I think was implied, I have no real argument with those points. I was just belaboring tangentially related thoughts. I should add that there are also several types of parthenogenesis not all involving only female organisms. This is well known to entomologists who study wasps for example, but getting into that would distort this thread beyond recognition.

It occurred to me that we're becoming splitters, in the continuum of lumpers to splitters. That said, in the defense of accuracy, so be it. But in terms of how to record superlative numbers, perhaps we can, as has been suggested at various times earlier, asterisk those anomalous candidates, whether they be twins*, multi-stems**, clones***, or whatever else we may come to consider in the future?-Don